In light of diminishing fossil energy reserves of fuels obtained from crude oil and stricter environmental protection requirements, increasing amounts of methyl or ethyl alcohol are being added to these fuels. Thus, any arbitrary refueling should be possible both with pure fuels and mixed fuels. When the alcohol content is higher, it is necessary to know the blending ratio in order to obtain optimal performance from the fuel-burning engine and to enable a precise proportioning of fuel adjusted to the operating conditions. The continuous determination of the alcohol content in the fuel fed into the fuel-burning engine in operation presents special problems for automobile engines in which any possible blend may be present by arbitrary refueling with various types of fuel.
The known optical processes are hardly suitable for this purpose since they often utilize interface effects to determine the refraction index, from which the alcohol content can be inferred. In addition to the difficulty of using these processes in automobile engines, another drawback of this process is that the mix to be observed must have a high homogeneity, especially at the interface. The required precision has not been achieved with this process.
Therefore, it has been proposed that the alcohol content in fuels be determined by means of a dielectric analysis. Such a process would solve the problem concerning measurement of the interface effects since measurement is done volumetrically. On the other hand, the conductance of the mixture significantly affects the volumetric dielectric analysis, i.e., cross sensitivity. Since the conductance is a function primarily of the pollutants or the water content, such a measuring process leads to useless results.
The possibility of determining the alcohol content of fuels by means of dielectric measurements is explored in the document "Proceedings of the Fourth International Symposium on Alcohol Fuels Technology," Sao Paulo, Brazil of Oct. 5, 1980. However, the process was rejected since the influences of temperature and conductance induced by water content or other pollutants in the fuel prevented a reliable measurement suitable for fuel-burning engines from being obtained.
Therefore, it is an object of the present invention to provide a process of the aforementioned kind which permits a precise and reliable determination of the alcohol content and/or calorific value in fuels, in particular for application in automobile engines.
Other objects and advantages are apparent from the specification and drawings which follow.